Patent application WO-A-00/37269 (or U.S. Pat. No. 6,640,589) proposed a resilient non-pneumatic tire characterised by a load-bearing structure essentially comprising a plurality of supporting elements arranged substantially radially in accordance with a cyclic symmetry around the circumference of the tire. When this tire is under load, a certain number of supporting elements present in the contact patch are subjected to major flexure, which enables them to absorb a proportion of the load. An interconnecting structure causes the supporting elements to work together by transferring the stress onto adjacent supporting elements. The load-bearing capacity of this use arises from the flexural stressing of the supporting elements present in the contact patch of the resilient non-pneumatic tire, and it also arises from the flexural stressing of the supporting elements outside the contact patch of the resilient non-pneumatic tire, via this interconnecting structure.
Although the resilient non-pneumatic tire proposed above has proved to be perfectly capable of bearing a major load in normal service, patent application EP-A-1 359 028 (or US-A-2003/0226630) has proposed an improvement to the above load-bearing structure by imparting thereto considerably improved endurance, while maintaining its very considerable load-bearing ability thanks to the introduction of a plurality of resilient articulated joints, each arranged at least in part between the diene elastomer interconnecting structure and the first part of each supporting element.
In this improved flexible tire, as illustrated in FIG. 1 of the above-mentioned application EP-A-1 359 028 and in the single FIGURE of the present application, the supporting elements or arches 2, comprising for example a stack of flexible composite material strips embedded in a rubber matrix, bear the load. They do not work entirely independently of one another, but are connected to one another by an interconnecting structure 3 surmounted by a tread 13, both made from a diene elastomer, with interposed resilient articulated joints 4 so as to ensure effective operation of the assembly, avoiding excessively intense shearing, and so as to provide good uniformity, i.e. relative constancy of properties whatever the circumferential position of the tire relative to the ground.
According to the teaching of said application EP-A-1 359 028, each resilient articulated joint 4 is itself preferably formed of a composition of diene elastomer such as those used for the sidewalls of tires (sufficiently low hysteresis and satisfactory tear strength), which enables the resilient joints to function correctly in their role of transmitting forces between the supporting elements 2 and the interconnecting structure, while withstanding major and repeated deformation. The excellent compatibility which exists between essentially unsaturated diene elastomers ensures in known manner very strong adhesion between the various parts.
Said application EP-A-1 359 028 specifies that another material capable of providing excellent results for this resilient articulated joint 4 is polyurethane.
As is known, polyurethane exhibits very many advantages, including excellent tensile strength, tear strength, resistance to abrasion and to chemicals, and, very particularly, low hysteresis.
One major disadvantage of polyurethane, however, resides in the difficulty of properly bonding this product to a diene elastomer part, as is moreover required by the structure of the non-pneumatic tire described above.
First of all, no effective method is yet known for bonding polyurethane to an uncured, unvulcanised diene elastomer.
While specific liquid polyurethane adhesives capable of bonding cured (i.e. polymerised) polyurethane to cured (vulcanised) diene rubbers are indeed available, this entails independently polymerising the polyurethane, on the one hand, and curing the rubber, on the other, before processing them together for bonding (cf. for example U.S. Pat. No. 4.942,093).
This solution is not satisfactory, in particular in the present case, due to the great number of drawbacks arising therefrom, some of which are unacceptable from an industrial standpoint and inimical to any attempt to achieve elevated production rates:                it is first of all necessary separately to prepare the above-described tread 13 and the interconnecting structure 3, both made from an uncured diene elastomer, on a rigid core;        an intermediate separate curing step for these diene elastomer parts, before contact with the cured polyurethane, must then be performed;        it must then be possible to apply the liquid polyurethane adhesive uniformly between two cured surfaces at a controlled thickness, while controlling unwanted flow of said adhesive;        without both mechanical and chemical preparation of the surface, such as brushing or scratching of the surfaces to be bonded followed by acid attack, it is impossible to bond the cured polyurethane properly to the cured diene elastomer;        finally, the level of adhesion achieved at high temperature, typically at a temperature of the order of 90° C. to 100° C., is known to be inadequate with regard to the requirements specific to a tire, whether non-pneumatic or pneumatic, for a road vehicle likely to run at sustained high speed.        